The invention relates to a high frequency instrument for incision and excision, and more particularly, to an instrument commonly referred to as a high frequency snare, high frequency knife or the like used to treat an affected part within a coeloma and which can be inserted into the coeloma to excise an affected part such as a polyp by cautery with high frequency current.
When it is required to effect excision of the tissues of an affected part which is located within the coeloma of a living body, for example, a polyp on the wall of the stomach, a high frequency instrument for incision and excision is inserted into the stomach together with an endoscope. The instrument is then moved close to the polyp and a loop which is formed on the distal end of a wire electrode of the instrument is caused to tightly bound the polyp. By passing high frequency current through the wire electrode, the polyp can be excised by cautery while observing it through the endoscope.
FIG. 1 shows one form of a conventional high frequency instrument for incision and excision. Specifically, the instrument includes a sheath 1 through which a wire electrode 3 is passed. The instrument is operated by an operating unit 2 which is mounted on the sheath 1 at the proximate end thereof. The sheath 1 and the wire electrode 3 are mounted on the operating unit so that the unit 2 cannot be rotated relative to the sheath 1 and the wire electrode 3. However, difficulties are experienced in that after mounting the operating unit 2 on the sheath, the unit 2 may be rotated. Such rotation is transmitted to the distal end through the wire electrode 3, whereby the semi-circular loop 4 located at the distal end can be twisted and become entangled around the affected part. Such difficulties can be overcome, for example, by providing as shown in FIG. 2, a fixture 5 which is connected to the proximate end of the wire electrode 3 and which is rotatable relative to the latter. Such a device is disclosed in Japanese Laid-Open Patent Application No. 78,655/1983. However, this results in the disadvantage that the semi-circular loop is again twisted and entangled with the affected part if the operating pipe 6 is rotated while the operating unit 2 is not mounted on the sheath 1. Such entangling prevents the tissue portion which is subjected to the cautery from being tightly bound in a reliable manner, and the passage of high frequency current cannot positively disconnect the tissue at the desired location. This causes the wire electrode to be seized with the tissue.